This invention relates to emergency release couplers for coupling together two pipes. The invention is particularly applicable to the coupling of a tanker loading or discharge pipe to an offshore installation or a shore-mounted pipe, for example a pipe mounted on a jetty. However, the coupler could be used in other contexts where two pipes are to be releasably coupled together.
Emergency release couplers usually form part of marine loading arm cargo transfer systems which are installed on jetties at marine terminals and which are used to connect a shore line to a tanker. Marine loading arms are used worldwide for loading and discharging all sizes of tankers with practically every type of hydro carbonate.
The loading arm usually consists of an articulated pipe structure connected to the tanker manifold by either a bolted flange or, more commonly, a tanker manifold coupler. The loading arms are moved into position and, where a coupler is fitted, coupled by hydraulic power. In recent years, when volatile products are being handled, it has been the practice to fit emergency release couplers behind the manifold coupler of the tanker.
Emergency release couplers consist of two valves, one each side of a band clamp coupler, and are used for rapid separation of a tanker from a loading arm with minimum spillage. The normal sequence of operation is to close the main product line valves, close the emergency release coupler valves and then to operate the band clamp coupler to the release loading arm. The tanker carries away the lower valve of the emergency release coupler system and pipe work to the coupler which are retrieved later and re-assembled to the loading arm.
On some liquid petroleum gas tankers and liquid natural gas tankers, a separate gas return line is incorporated in the system. This line also has an emergency release coupler so that both lines may be severed in an emergency.
A typical emergency, when the emergency release couplers are operated, is when a tanker breaks its moorings and drifts off the jetty due to external forces, requiring the rapid severence of the loading arm with minimum spillage.
An emergency release coupler is known which comprises two ball valves and a band clamp. The top valve is operated by a hydraulic cylinder and the other valve is operated by a push rod system. The coupler is operated by a separate hydraulic cylinder and relies on sequence valves to control the operation. This system has proved not to be one hundred per cent reliable owing to faults in the hydraulic system.
In another known system having a gas return line, the gas return line has a separate emergency release coupler and from the lower valve there is a flexible pipe connection to the tanker manifold. In an emergency, the disconnected gas return line and valve, the lower portion of the emergency release coupler unit, falls two to three metres onto the deck of the tanker. The product line coupler units and the gas return line coupler units have separate hydraulic circuits and have to be controlled by sequence valves. This system has also proved to be less than satisfactory.